Compounding and vulcanization of synthetic rubber



Patented May 7,1946 v I comrotmpmo AND VULCANIZATION F SYNTHETIC RUBBER 'Albert A. Sonnet-ville, Carmel, n. in, aeslgn'or to R. '1. Vanderbilt Company, Inc., New York,

N. Y a corporation of New York No Drawing.' Application February r1, 1944, Serial No. 522,181;

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.My invention relates to improvements in the compounding and vulcanization of synthetic rub, bers produced by copolymerization of butadiene and styrene. Synthetic rubbers of this type are illustrated by the copolymer product currently designated GR-S rubber. In my application, Serial No. 522,785, filed February 17, 1944 I have described my discovery that the addition of 0.005 1%, more suitably (ml-0.5%, of copper (as such or in the form or an appropriate compound) to compounds of this type of synthetic rubber afford important improvements, with respect to rate of cure and variability, particularly in rate of cure, when these compounds are vulcanized with sulfur, as such, in amount exceeding that required to form cupric sulfide with the copper present. I have found that copper is with advantage added to compounds of such, synthetic rubber, in applying my discovery, as a predispersion of a copper salt on. an inert filler such as carbon black, clay or chalk. Dispersion of the copper in the synthetic rubber compound is thus facilitated while particles of metallic copper are eliminated from the compound. In one aspect the inert filler c rying the copper salt itself constitutes a new and valuable compounding material.

The following examples will illustrate practices embodying my invention and include comparisons indicating some of its advantages. In the tabulations of these compounds, cures and physical properties, the compound or each example was made up of the number of parts by weight indicated opposite each designated component, the cures were in a platen press for the periods indicated in minutes at the left under the curin temperature, all 01' the cures in each group being eilected at the same temperature, and, for each period of cure, the values for stress at 300% elongation. in pounds per square inch appear under "8." for tensile strength in pounds per square inch under 'I," for percentage elongation at Pigs}: under E, and for Shore hardness under Example I Example 11 The foregoing Examples I and II illustrate the application of my invention with a carbon black carrier. The modified carbon black of Exampl 11 was thesame black used in Example I after being made into a slurry with a gasoline solution of copper oleate in amount suillcient to load the black with about 0.2% by weight on'the black-of copper sulfate measured as copper, dried and round. v

Example 111 Example IV Example V 100 1(1) 100 6 6 5 5 5 5 Ill 2 2 2 Benzothiazyldisulfldm l. 5 l. 5 l. 5 Zinc diethyldithiocarbamate .15 ..15 .15 Clay 100 100 Clay modified 100 Copper powder (through 1 300 mesh) 1 307F. BTEHSIEHSTEH 10 minutes Lncured 400 625 76050375 650 700 46 15 minutes 176 225 575 38 5%) 995 150 56 470 810 720 51 20 minutes 240 305 860 30 566 1000 700 57 676 960 785 54 30 minutes 340 486 700 42 010 1010 650 58 675 1010 720 55 The foregoing Examples 111, IV and 'v illustrate the application 01' my invention with a clay carrier. The modified clay of Example IV wasthe same clay used in Example 111 after being made into a slurry with an aqueous solution of copper sulfate in amount sufficient to load the clay with about 0.1% byweight on the clay of copper sulfate measured as copper, dried and ground.

Comparing Example 11 with Example I, and again comparing Example IV with Example III, the acceleration oi! the rate'oi cure will be apparent. The savings in time required for vulcanization of products from such stocks shown by these comparisons are an important economy. These same comparisons also show, in addition 7 to this saving of time, substantial improvement 60 uration.

in the physical properties '01 the vulcanizates.

It will also be noted, comparing Example IV to Example V, that the modified clay produces phys lcal properties somewhat superior to those pro-' duced by the'separate use oi the clay and the equivalent amount of metallic copper. The parts by weight on the GR-S rubber of added copper, measured as copper, is the samein Example IV and Example V.

Chalk can be processed in the same way as clay to form' a carbonate filler carrying a copper salt.

The copper loading may be applied to the inert filler as just described using any soluble copper salt in a volatile solvent which does not react with the filler. The predispersion of the copper salt upon the filler may also be accomplished by trit- Copper carbonate, copper sulfate or copper stearate, for example, may be disin'ibuted upon the filler in this manner. I include copper soaps: within" the term copper salt" herein.

The plasticizer used in the foregoing examples was a mixture or 15 parts by weight or a petroleum sulfonate', 5. parts of normal butyl alcohol and 30 parts of a viscous petroleum oil (currently sold under the trade-name Reogen) The proportion of sulfur used is not critical and may follow conventional practices providing it is added to the compound subjected to vulcanization in amount exceeding that required to combine with the added copper to form cupric sulfide.

I claim:

1. A vulcanizable compound comprising a rubbery copolymer of butadiene and styrene, a chemically inert filler carrying a copper salt, and an amount of sulfur exceeding the amount required to convert all of the copper to cupric sulfide, the total copper content of the compound being not less than about 0.005% nor more than about 1% on the weight of the copolymer.

2. The product of vulcanization of a compound comprising a rubbery copolymer of butadiene and styrene, a chemically inert filler carrying a copper salt, and an amount of sulfur exceeding the amount required to convert all of the copper to cupric sulfide, thetotal copper content of the compound being not less than about 0.005% nor more than about 1% on the weight of the copolymer.

3. A vulcanizable compound comprising a rubbery copolymer of butadiene and styrene, carbon black carrying a copper salt, and an amount of sulfur exceeding the amount required to convert all of the copperto cupric sulfide, the total copper content or the compound being about bill-0.5%

on the weight of the copolymer.

4. The product of vulcanization or a compound comprising a rubbery copolymer of butadiene and styrene, carbon black carrying a copper salt, and an amount of sulfur exceeding the amount required to convert all of the copper to cupric sulflde, the total copper content of the compound being about 0.01-0.5% on the weight or the copolymer.

a 5. A vulcanizable compound'comprising a rubbery copolymer of butadiene and styrene, clay carrying a copper salt, and an amount of sulfur exceeding the amount required to convert all of the copper to cupric sulfide, the total copper content of the compound being about OBI-0.5% on the weight of the copolymer.

6. The product of vulcanization of a compound comprising a rubbery copolymer of butadiene and styrene, clay carrying a copper salt, and an amount of sulfur exceeding the amount required to convert all or the copper to cupric sulfide, the total copper content of the compound being about Obi-0.5% on the weight of the copolymer.

7. A vulcanizable compound comprising a rubbery copolymer of butadiene and styrene, chalk carrying a copper salt, and an amount of sulfur exceeding the amount required to convert all of ALBERT A. SOMERVILLE. 

